What Is Littermate Syndrome? – VET VERIFIED!

This article has been edited and verified by our own veterinarian Dr.Stevce Ilievski. 

Are you considering raising two or more littermate puppies? It may sound like a fun idea, but many experts would advise against it. That’s because it is said to lead to the so-called littermate syndrome (also known as littermate/sibling aggression).

But, what is littermate syndrome?

We’ve tried delving deeper into this controversial topic to answer this question and many more.

What Is Littermate Syndrome?

The term littermate syndrome in dogs refers to behavioral issues in puppy siblings or unrelated puppies of the same age. This is also known as sibling syndrome in dogs and occurs when puppies are raised in the same household beyond 8–10 weeks of age. 

This occurs when the dogs become so closely connected to each other that when separated have trouble socializing with other dogs and/or humans and prefer each other’s company instead.

However, the littermate syndrome aggression may also be directed toward each other, especially if they are same-sex siblings. 

All of this also means that setting boundaries and training, essential parts of basic dog care, are likely to become much more challenging. 

How Common Is Littermate Syndrome?

No scientific data provides an exact answer to this question or even an official diagnosis. That’s why some sources claim that dog sibling syndrome is a myth

The closest answer we can give you is that the syndrome isn’t guaranteed, but it’s quite common according to everyday observations.

What are the symptoms of littermate syndrome?

There is not one littermate syndrome in dogs, but several. However, here are some of the main ones:

  • Fear of unknown people, animals, and places
  • Anxiety when separated from their sibling(s)
  • Difficulty with training
  • Crate issues
  • Refusing to eat alone

How to Prevent Littermate Syndrome

Considering everything we discussed so far, it’s fairly obvious that keeping littermates separate for a notable amount of time during the critical period is crucial. The activities during which they should be separated include:

  • Feeding
  • Walking
  • Training
  • Grooming
  • Playing with the owner
  • Sleeping

Can Littermate Syndrome Be Cured?

Fixing the syndrome is hard, but it isn’t impossible. Of course, the sooner you start the higher the chances of succeeding, so if you’ve noticed some of the potential symptoms, act immediately.

All the steps we just listed above should be followed, but if the puppies’ attachment is already super strong, you must do this gradually.

You should also consider consulting an animal behavioral specialist and getting professional help. After all, things can be difficult in the beginning even with one puppy, so don’t hesitate to ask for help.

Do Puppies Overcome Littermate Syndrome With Age?

Puppies don’t outgrow this behavior naturally. On the contrary, littermate syndrome in older dogs can worsen if you don’t try to prevent it earlier. This is why reacting as soon as you notice the first symptoms is crucial.

What If You Already Have Littermates?

Don’t panic! It’s not the end of the world. There are a lot of things you can do to help alleviate this. Let’s take a look at exactly what you can do.

1. Train them separately

If you’ve already adopted two dogs, the first thing that you need to do is to train them separately. Although this might be easier said than done, just be patient with them, and give it some time. Not only does this make the entire process easier on you or the person training the dogs, but it teaches the dogs to get used to being on their own.

2. Separate meal times and bowls

The second thing you should do in this situation is to have separate meal times and bowls for both puppies. Although this might be difficult if you’re a single dog parent, providing separate food bowls for both puppies is imperative. This will teach your dogs to be okay without their brother/sister.

3. What about a third dog?

There are some owners who say that getting one more dog (an older dog) helped solve the littermates syndrome. This dog would apparently limit the other puppy’s bonding time, although there is no concrete evidence of this.

4. Should you consider rehoming?

You should only consider rehoming one or both puppies if they’re constantly fighting, which can often lead to severe injuries or death. However, this should always be taken as a last resort and after consulting with a vet or a pet behaviorist.


What causes littermate syndrome?

The causes are not entirely clear, but some theories state that it may happen when the owners assume that two puppies can fulfill each other’s socialization needs, so they don’t spend enough time with them individually. 

Are there any littermate syndrome studies?

There is no scientific evidence to prove this syndrome is real. However, we did find some information about an experiment organized by a guide dog organization.

It involved two groups: those in group one were given two puppies to raise while those in group two were given just one puppy. It’s important to note that the dogs were temperament-tested first. 

The results show that getting two puppies from the same litter always caused one of them to become temperamentally unsuitable for work, even if both started off as ideal candidates.

That being said, it’s important to mention that we don’t know whether the foster family had any experience raising two dogs at once and how much time they dedicated to working with them individually.

Can dogs recover from littermate syndrome?

If you notice the symptoms linked to littermate syndrome (especially if it’s earlier on), you can try to correct them. It takes lots of time and effort, but it isn’t impossible if you follow the suggestions we listed above.

How to stop littermates from fighting.

You can do a few things to try and stop littermates from fighting. The most important thing is to be consistent in enforcing rules and limits. Make sure both dogs know what is and is not allowed, and keep them separate when you are not able to supervise them.

You can also try using positive reinforcement, such as treats or praise, to encourage good behavior. If the fighting continues, you may need to seek professional help from a behaviorist or trainer.

Final Thoughts

If you’ve read our article carefully, you’ve probably come closer to answering the question of what is littermates syndrome, as well as how to avoid it. If not, then perhaps the best thing you can do is wait at least 6 months to get the second one — or consider getting adult dogs

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